1. Technical Field
The present invention is directed to plant acyltransferase-like nucleic acid and amino acid sequences and constructs, and methods related to their use in altering sterol composition and/or content, and oil composition and/or content in host cells and plants.
2. Related Art
Through the development of plant genetic engineering techniques, it is now possible to produce transgenic varieties of plant species to provide plants which have novel and desirable characteristics. For example, it is now possible to genetically engineer plants for tolerance to environmental stresses, such as resistance to pathogens and tolerance to herbicides. It is also possible to improve the nutritional characteristics of the plant, for example to provide improved fatty acid, carotenoid, sterol and tocopherol compositions. However, the number of useful nucleotide sequences for the engineering of such characteristics is thus far limited.
There is a need for improved means to obtain or manipulate compositions of sterols from biosynthetic or natural plant sources. The ability to increase sterol production or alter the sterol compositions in plants may provide for novel sources of sterols for use in human and animal nutrition.
Sterol biosynthesis branches from the farnesyl diphosphate intermediate in the isoprenoid pathway. Sterol biosynthesis occurs via a mevalonate dependent pathway in mammals and higher plants (Goodwin, (1981) Biosynthesis of Isoprenoid Compounds, vol 1 (Porter, J. W. & Spurgeon, S. L., eds) pp. 443-480, John Wiley and Sons, New York), while in green algae sterol biosynthesis is thought to occur via a mevalonate independent pathway (Schwender, et al. (1997) Physiology, Biochemistry, and Molecular Biology of Plant Lipids, (Williams, J. P., Khan, M. U., and Lem, N. W., eds) pp. 180-182, Kluwer Academic Publishers, Norwell, Mass.).
The solubility characteristics of sterol esters suggests that this is the storage form of sterols (Chang, et al., (1997) Annu. Rev. Biochem., 66:613-638). Sterol O-acyltransferase enzymes such as acyl CoA:cholesterol acyltransferase (ACAT) and lecithin:cholesterol acyltransferase (LCAT) catalyze the formation of cholesterol esters, and thus are key to controlling the intracellular cholesterol storage. In yeast, it has been reported that overexpression of LRO1, a homolog of human LCAT, and phospholipid:diacylglycerol acyltransferase increased lipid synthesis (Oelkers et al., (2000) J. Biol. Chem., 26:15609-15612; Dahlqvist et al., (2000) Proc. Natl. Acad. Sci. USA, 97:6487-6492).
The characterization of various acyltransferase proteins is useful for the further study of plant sterol synthesis systems and for the development of novel and/or alternative sterol sources. Studies of plant mechanisms may provide means to further enhance, control, modify, or otherwise alter the sterol composition of plant cells. Furthermore, such alterations in sterol content and/or composition may provide a means for obtaining tolerance to stress and insect damage. Of particular interest are the nucleic acid sequences of genes encoding proteins which may be useful for applications in genetic engineering.